The invention relates to a double-seat valve having a seat-cleaning function having two serially disposed closing elements that are movable relative to each other that in the closed position of the double-seat valve prevent an overflow of fluid from one valve housing part into another and that in the closed as well as in the open position define a leakage cavity, which has a drain outlet leading downward, relative to a vertical arrangement of the double-seat valve, out of the associated valve housing part, having the first closing element that is designed as a slide piston and is driven independently and in its closed position rests, forming a seal, in the connecting opening joining the valve housing parts together, and during its opening movement comes into contact in a sealing manner with a second closing element assigned to the second seat, and carries this also into the open position, having a first seat seal arranged in the first sealing element that seals radially against a cylindrical first seat formed in the connecting opening, having the closing elements that can be moved gap-wide independently of each other by a partial lift, in each case, into a seat cleaning position for the purpose of flushing their seats, wherein the second closing element can be moved by a second partial lift in the same direction as the opening movement, and the first closing element can be moved by a first partial lift in the direction counter to the opening movement into its respective seat cleaning position, and having valve rods, arranged concentrically inside each other, for the closing elements that are led upward into a common drive, and having a tubular shaft, arranged at the lower lying closing element, that penetrates the associated valve housing part radially outside downward in a sealing manner, and that connects the leakage cavity radially inside via a drain to the surroundings of the double-seat valve, and that merges upward into the valve rod of the lower lying closing element.
The second closing element can also be equipped as a slide piston with radially acting sealing means, wherein the associated cylindrical second seat is formed in the connecting opening. However, the second closing element can also be implemented as a seat plate that seals axially or axially/radially on an assigned planar or conical second seat. Double-seat valves having a seat-cleaning function with the initially listed features open either upward (normal case) or downward into the fully open position. For an upward opening double-seat valve, the independently driven first closing element is disposed at the bottom, and for the reverse opening direction, the independently driven first closing element is disposed at the top.
From the German patent DE 38 35 944 C2, a double-seat valve having a seat-cleaning function is known, in which the independently driven first closing element is designed as a slide piston, and can be transferred during the associated seat cleaning by a first partial lift, in the direction counter to the opening movement, into its seat cleaning position (FIG. 3). The dependently driven second closing element is implemented as a seat plate, which seals on an associated conical seat, and it is transferred by a second partial lift, in the same direction as the opening movement, into its seat cleaning position, in which an annular gap that is open from below upward, relative to a vertical assembly position, is formed between closing element and associated seat.
A tubular shaft of the first closing element, located at the bottom, that penetrates through the lower valve housing part in a manner sealing towards the bottom, is enlarged in the movable penetration area into a cylinder, a so-called pressure balancing piston, such that an annular surface that is approximately equal to the adjacent annular surface on the lower side of the first closing element, results on the top side of the pressure balancing piston. When the first closing element is moved downward into the seat cleaning position, a circular-shaped gap that is open from above downward is formed between the outer surface of the pressure balancing piston and a lower annular collar of the lower valve housing part, and via this gap the outer surface can be flushed simultaneously with the first closing element. In connection with a pot adjacent to the annular collar, furthermore, a flush device is formed with which the pressure balancing piston on the lower, first closing element can be cleaned completely so that displaced product in the passage area can be cleaned reliably at full opening and closing lift. A cleaning of the valve rod of the upper, second closing element in the area of its passage through the associated valve housing part is not provided.
The patent EP 0 587 690 B1 describes a double-seat valve having two closing elements, each constructed as a slide piston. The double-seat valve opens from above downward, relative to a vertical assembly position. The valve rods provided for actuation of the two closing elements are both guided upward out of the associated valve housing part and into a common drive. The hollow rod of the upper, first closing element is expanded in its penetration area with the valve housing into a pressure balancing piston, and this penetration area is provided with a flush device, so that a sufficiently large axial extension area of the pressure equalization piston can be subjected to cleaning if required. The lower, second closing element is elongated into a tubular shaft formed likewise as a pressure balancing piston, which is guided downward out of the associated valve housing part, in a sealed manner. In a preferred embodiment, this penetration location also is assigned a flush device so that a sufficiently larger axial extension area also of this pressure balancing piston can be subjected to cleaning.
The double-seat valve above is only capable of seat cleaning under certain conditions, i.e., its seats do not open gap-wide by a respective partial lift. Rather, for cleaning the seats, the associated closing elements are pushed only so far in the same direction, or counter direction, that the respective partially exposed seats can be subjected to cleaning fluid (so-called wipe cleaning). The provisioning of cleaning fluid occurs in that with a partial lift, in the direction counter to the complete opening lift of the double-seat valve, the passage of the pressure balancing piston associated with the respective closing element is also exposed such that the flow of cleaning means is branched off through the exposed passage out of the valve housing part, and in the process cleans this passage and at least one of the following areas, namely the other passage, the leakage cavity and the accessible seat.
In the following, the term rod passage shall include, along with the passage of the valve rod through the associated valve housing part, also the passage of the tubular shaft, arranged on the lower lying closing element, penetrating downward through the associated valve housing part. It can be stated in principle that the rod passage, or the passage of the pressure balancing piston provided in this area into which the valve rod or the tubular shaft respectively can be expanded where necessary, of the independently driven closing element is more critical than the corresponding passage with the dependently driven closing element. This results from the fact that during the opening lift the independently driven closing element always moves in the direction of the dependently driven closing element, and as a result the associated valve rod or the rod shaft or the associated pressure balancing piston, of the independently driven closing element is pushed out of the penetration area into the interior of the associated valve housing part. With respect to the dependently driven closing element, the reverse conditions arise; parts of the valve rod or rod shaft or the associated pressure balancing piston in this area are, in the scope of the movement of the opening lift, pushed out of the interior of the associated valve housing part into the penetration area. If product is present in both valve housing parts, then during the opening and closing lift a carryover of the product into the associated penetration areas of the rod passages of both closing elements possibly results. However, if cleaning fluid is present in the course of seat cleaning, then the parts of the valve rod or of the rod shaft or the associated pressure balancing piston of the dependently driven closing element, extending into the valve housing part, are already cleaned, and as a result are moved in a cleaned state into the passage during the opening lift or during partial lift.
With the known double-seat valve according to EP 0 587 690 B1, as with all other double-seat valves that open downward and have a leakage drain guided downward out of the valve housing (for example, the double-seat valve according to EP 0 646 741 A1), it is advantageous that in the open position of the double-seat valve, the passage cross-section of a connecting opening connecting the two valve housing parts together is not constricted by the cross-section of the leakage drain outlet that is formed as a tubular shaft and is disposed at the lower lying closing element. This then, reduces in particular the nominal width of the valve housing, determined by the passage cross-section of the connecting opening, by 1 to 2 nominal widths if, for example as required in the USA, the passage cross-section of the leakage drain outlet between the leakage cavity and the surroundings of the double-seat valve must be equal to the largest passage cross-section of the tubing attached to the double-seat valve.
The double-seat valve of the initially described type having a seat-cleaning function, desirably has a sufficient cleaning of the passage of the valve rod or of the valve rod expanded to a pressure balancing piston, of the independently driven closing element, as well as to specify a method for cleaning this double-seat valve having a seat-cleaning function.